JP1999-321153A describes a conventional sheet supplying device of this kind. The conventional sheet supplying device constitutes a part of a sheet accumulating apparatus shown in FIG. 5. Referring to FIG. 5, the sheet accumulating apparatus comprises a sheet feed section A, an inverting transport section B, a transport section C and an accumulation section D. Placed on the sheet feed section A is a sheet stack configured by stacking plural sets of sheets collated by page order, each of which corresponds to one volume. Then, sheets are sequentially fed for each set of sheets from the sheet feed section A in a state where the sheets are superimposed on one another so as to be sequentially offset from one another in a fore-to-aft direction. After that, the sheets are vertically inverted by the inverting transport section B, and are transported to the accumulation section D through the transport section C. In the accumulation section D, the received sheets are collated and accumulated as a set of sheets, which corresponds to one volume, and then, are supplied to a bookbinding machine (not shown).
A sheet supplying device is arranged in the sheet feed section A. The sheet supplying device comprises a vertically movable sheet table 30 on which a stack of sheets P is placed, a sheet feeding belt mechanism 31 which transmits the sheets P to the inverting transport section B, and a reverse belt mechanism 32 which is placed in parallel with the sheet feeding belt mechanism 31.
The sheet feeding belt mechanism 31 includes a drive motor 31a, a drive pulley 31b coupled to a drive shaft of the drive motor 31a, a pair of auxiliary rollers 31c, 31d, and an endless belt 31e extending among the drive pulley 31b and the pair of auxiliary rollers 31c, 31d. When the drive motor 31a is operated, the endless belt 31e are rotated and driven in a counterclockwise direction, so that the sheets P are transported one by one in a transport direction.
The reverse belt mechanism 32 includes a drive motor 32a, a drive pulley 32b coupled to a drive shaft of the drive motor 32a, a pair of auxiliary rollers 32c, 32d, and an endless belt 32e extending among the drive pulley 32b and the pair of auxiliary rollers 32c, 32d. When the drive motor 32a is operated, the endless belt 32e is rotated and driven in a clockwise direction.
In this case, during the sheet feeding operation, the sheet table 30 gradually moves upward, and a top surface of the sheet P in the uppermost position of the sheet stack is always in contact with the endless belt 31e of the sheet feeding belt mechanism 31 and the endless belt 32e of the reverse belt mechanism 32.
A sensor 33 for detecting a sheet is arranged in the rear of the sheet table 30. The sensor 33 includes a light emitting element 33a and a light receiving element 33b. Also arranged in the rear of the sheet table 30 is a duct 34 which jets air for separating sheets of the upper layer of the sheet stack one by one.
Thus, the sheet P in the uppermost position of the sheet stack placed on the sheet table 30 and separated therefrom by the air is moved rearward by the reverse belt mechanism 32. Then, when the sheet P in the uppermost position is moved to a detection position of the sensor 33, the reverse belt mechanism stops and, also, the sheet feeding belt mechanism 31 starts to operate on the basis of a sheet detection signal from the sensor 33. With the above operations, the sheet P in the uppermost position is transported forward to the inverting transport section B.
By repeating the above operations, a set of sheets, which corresponds to one volume, is fed in a state where the sheets are superimposed on one another so as to be sequentially offset from one another in a fore-to-aft direction.
In addition, when the sensor has detected double transportation of sheets, the sheet supplying device is stopped and the transportation error is modified. In addition, measurement of the number of sheets to be fed is used for determination on whether a set of sheets, which corresponds to one volume, has been fed.
An inverting transport device is arranged in the inverting transport section B. The inverting transport device includes a rotary drum 35 of a large diameter, a drive roller 35c and driven rollers 35a, 35b which are arranged so as to surround half of the circumference of the rotary drum 35, and an endless belt 35d which extends among these rollers 35a to 35c and a part of which is brought into contact with a periphery of the rotary drum 35 by pressure. Then, an aggregation of sheets fed from the sheet feed section A by the sheet feeding belt mechanism 31 is transported between the rotary drum 35 and the endless belt 35d from downside of the periphery of the rotary drum 35, during which the sheets are inverted vertically. Then, the sheets are transmitted to the transport section C from an upper position of the periphery of the rotary drum 35.
The transport section C includes a drive roller 37 arranged just before the accumulation section D and an endless belt 36 extending between the roller 37 and the rotary drum 35. In addition, a pair of auxiliary rollers 39 are brought into contact with the lower orbit of the endless belt 36. The endless belt 36 performs circumferential motion between the drive roller 37 and the rotary drum 35 at the same speed as peripheral velocity of the rotary drum 35. Pressing rollers 37a, 37b, 37c are arranged so as to be spaced from one another on the upper part of the endless belt 36. Thus, an aggregation of sheets vertically inverted, which corresponds to one volume, is transported by the transport section C.
When the aggregation of sheets is transferred from the transport section C to the accumulation section D, the aggregation of sheets is stacked in the accumulation section D, sequentially from a bottom sheet constituting the aggregation, with the edges of the sheets jogged as the end of the sheet abuts a jog plate 38. The sets of sheets accumulated in the accumulation section D are fed to the bookbinding machine.
Such a conventional sheet supplying device has an advantage that as a set of sheets, which corresponds to one volume, is transported In a state where the sheets are superimposed on one another so as to be sequentially offset from one another in a fore-to-aft direction, the sheet accumulating speed is fast even when the transport speed is rather slow, and that a trouble is less likely to occur in the process of sheet transportation or accumulation. However) as the response speed of the sheet feeding belt mechanism and the reverse belt mechanism is slow when their actuation/stop is switched, it is difficult to determine timing of switching operations of the sheet feeding belt mechanism and reverse belt mechanism. In addition, since the sheets are transported by circumferential motion of the belt, there has been a problem that a slip of a sheet impedes reliable transport of the sheet, so that the feeder is prone to a feed error.